FIG. 9 shows the arrangement of a conventional electrophotographic as an example of a printing apparatus of this type.
Referring to FIG. 9, reference numeral 1 denotes a photosensitive drum for forming an electrostatic latent image; 2, a charging roller for uniformly charging the photosensitive drum 1; 5, an optical unit for generating a laser beam which scans the surface of photosensitive drum 1 upon exposure; 6, a laser beam emitted by the optical unit 5; 3, a developer for developing an electrostatic latent image formed on the photosensitive drum 1, by toner; 4, a transfer roller charger for transferring a toner image on the photosensitive drum 1 onto a predetermined paper sheet; 7, a fixing device for melting and fixing toner on the paper sheet; 8, a standard cassette for storing a stack of paper sheets used in a print process; 9, a standard cassette feed roller for picking up a paper sheet from the standard cassette; 10, a manual insert tray; 11, a manual insert feed roller; 12, exhaust rollers for exhausting the paper sheet outside the apparatus; 13, a registration sensor for registering the leading end of a fed paper sheet in a print process; 14, an exhaust sensor for confirming if a paper sheet has normally been exhausted from the fixing device; 15, a sensor for detecting the presence/absence of paper sheets in the standard cassette; 16, a sensor for detecting the presence/absence of paper sheets to be manually inserted; 17, a toner cartridge (expendable) which integrates the photosensitive drum 1, charging roller 2, developer 3, and toner, and is detachable from the printer main body; 21, a nonvolatile memory mounted on the cartridge; 19, a connector for exchanging signals with the nonvolatile memory 21; and 20, a printer control unit for reading/writing data from/to the nonvolatile memory via the connector.
In the above arrangement, the nonvolatile memory 21 is mounted in the toner cartridge 17, and a printer engine writes data that pertains to the use state and the like of the cartridge in the memory so as to make control for managing on the basis of written data, e.g., the service life or the like of the photosensitive drum.
FIG. 10 is a block diagram showing the contents of the printer control unit 20 in FIG. 9 and its peripheries.
Referring to FIG. 10, reference numeral 101 denotes a printer controller for receiving image data via communications with a host computer, mapping the received image data to information that the printer can print, and exchanging signals with a printer engine controller (to be described below) via serial communications; and 102, an engine controller for exchanging signals with the printer controller via serial communications to control respective units of a printer engine. Reference numeral 103 denotes a paper feed controller for executing paper feed control when a paper sheet to be printed is fed and conveyed until the paper sheet is exhausted after the print process, on the basis of an instruction from the engine controller 102; 104, an optical system controller for executing drive control of a scanner motor and laser ON/OFF control on the basis of an instruction from the engine controller 102; 105, a high-voltage system controller for executing high-voltage output control required for electrophotographic processes such as charging, development, transfer, and the like on the basis of an instruction from the engine controller 102; 106, a fixing temperature controller for executing temperature control of the fixing device on the basis of an instruction from the engine controller 102, and detecting any abnormality or the like of the fixing device; 107, a paper sensor input unit for transferring information from the paper sensors in the paper feed unit and paper convey path to the engine controller; 108, a jam detector for detecting convey errors during paper convey; and 109, a failure detector for detecting any failure of a functional unit in the printer. Reference numeral 17 denotes the toner cartridge which is detachable from the printer engine, as described above. The toner cartridge 17 has a nonvolatile memory 21 which can exchange data with the engine controller 102, and allows the engine controller 102 to read out or write data. Further, the printer controller 20 corresponds to the engine controller 102 and the other controllers 103 to 109.
The engine controller 102 reads out or rewrites the memory contents of the nonvolatile memory 21 on the basis of the command of the printer controller 101 or each detecting unit. Note that the rewritable nonvolatile memory uses an EEPROM, but other devices, for example, a flash memory and the like, may be used.
FIG. 11 shows signals exchanged between the printer control unit 20 and nonvolatile memory 21. The printer control unit 20 includes a CPU, which is connected to the nonvolatile memory 21 in the toner cartridge 17 by serial communication lines via a drawer connector.
The serial communication lines are formed of TDATA serving as command data to be output from the printer control unit 20 to the nonvolatile memory 21, RDATA serving as return status from the nonvolatile memory 21, and SCLK serving as a sync clock.
TDATA is issued when the printer control unit 20 reads out the contents of the nonvolatile memory and rewrites its contents, and a read/rewrite instruction is set using command bits. The read address and rewrite data are output serially. In response to a read command, the nonvolatile memory 21 returns its address and data (or may return data alone). In case of a rewrite command, the address and write data are transferred.
The nonvolatile memory 21 has only a read/write function. For example, it is conceivable that when the printer control unit 20 writes data such as the service life of the toner cartridge 17 or the like, which is important in terms of control, even if that data is inadvertently rewritten due to the influence of some operation errors, it is required to be able to recover the important data. For this purpose, areas where important data is to be written are assigned to a plurality of addresses, and even when the contents of a given area are rewritten, data can be controlled to be recovered or prevented from being lost by reading information at another address.
However, the method of storing important data upon controlling the printer engine, e.g., data that pertains to the service life of the cartridge, at a plurality of address positions, the nonvolatile memory requires a large capacity and will result in an increase in cost of the system. Furthermore, for obtaining a reliable data, data of plurality of address positions must be read out for finding errors, and if an error occurs, the data of a subject read corrected by using the plural data is restored.